1. Field of the Invention
This invention is directed to the production and use of certain arachidonic acid (ARA) rich microalgae for or in animal feeds and human foods. Such sources of arachidonic acid may be important for the enrichment of feeds used in agriculture, as they are vegetarian in nature and a renewable resource. There is a particularly important application in the field of aquaculture, as this environment is particularly depleted in sources of long chain omega-6 fatty acids, such as ARA. The algae can be produced in conventional autotrophic productions schemes or adapted, or engineered, to growth under heterotrophic conditions. The algae can be used as a feed directly through pelleting or compounding with other conventional feed sources, or used indirectly as a particulate for the enrichment of zooplankton (e.g., Artemia and rotifers) or other form of bioencapsulation, which are then consumed by the fish, crustaceans or mollusks. The ARA-rich algal biomass can also be processed to produce a pure triglyceride containing the ARA and delivered to humans or animals directly as the crude or refined oil. Other lipids and byproducts removed during the processing of the algal oil as well as the oil-extracted biomass can also be used as a feed ingredient.
2. Description of Related Art
Many seed oils are highly enriched in the 18-carbon, di-unsaturated, omega-6 fatty acid, linoleic acid (LA), and some even contain the 18-carbon, tri-unsaturated omega-6 fatty acid, gamma linolenic acid (GLA). However, terrestrial plants in general do not produce significant quantities of the 20-carbon, tetra-unsaturated, arachidonic acid (ARA). ARA is generally considered a fatty acid of animal origin and is an integral component of the structure, physiology and general biochemistry of most animals. For example, ARA makes up at least 20% of the fatty acid structure of the lipids of the gray matter of the brain in mammals. Consequently, all herbivorous animals have the ability to convert the dietary LA into ARA through elongation and desaturation enzymes inherent in those species. During periods of an animal's life history, however, preformed dietary ARA may be required due to a particularly high requirement for the ARA. Such a situation occurs, for example, in human infants where there is a period of accelerated brain growth and a requirement for large quantities of this building block of brain tissue. In this case, preformed ARA is delivered from the mother across the placenta to the fetus in utero and through the breast milk when the infant is nursing. Thus, sources of ARA are being sought for the supplementation of infant nutrition products to provide the ARA needed by the growing infant in a form similar to what it would get naturally from its mother.
Although the terrestrial environment is dominated by plants that are rich in omega-6 fatty acids other than ARA, it is deficient in plants that produce large amounts of omega-3 fatty acids. Thus, terrestrial animals, herbivores in particular, tend to be omega-3 deficient. The marine environment, on the other hand, is dominated by plants (phytoplankton and seaweeds) that are rich in omega-3 fatty acids, but are generally deficient in plants that produce large amounts of omega-6 fatty acids. Thus, marine animals, herbivores in particular, can potentially be omega-6 deficient, and particularly ARA deficient. Heretofore, this fact has not been recognized.
The consequences of omega-3 deficiency in the terrestrial animal diet (particularly man) have been well studied and it is believed that the effects of many of our chronic illnesses may be relieved in part by increasing the omega-3 intake in our diet (ie., lowering the ratio of omega-6 to omega-3 fats in our diet). Hyperimmune responses, platelet aggregation, and vasoconstriction are all thought to be related to excessive amounts of omega-6 fats in our diet. In an omega-6 deficient diet, that was replete in omega-3 fatty acids, immunosuppression, increased bleeding times and vasodilatation can be problematic. Since such an omega-6 deficient situation exists in most marine diets, the supplementation of ARA to such a diet should improve health and resistance to disease. This, in fact, was shown to be the case when an ARA-enriched dietary supplement was added to the regular diet of the marine fish Sea bream. In this case, there was an unexpected improvement in resistance to stress and disease when the ARA-supplement was used in this omega-6 deficient situation. Several products have now been offered for sale as aquaculture products containing supplements of ARA. These include VEVODAR™ (DSM, The Netherlands) and AQUAGROW™ AA (Martek Biosciences Corp, USA).
Both of the above mentioned products are produced using an ARA-rich oil from the cultured filamentous fungus Mortierella alpina. The fungus is grown according to procedures well established in the art and the ARA-rich oil is extracted and used for various purposes. In the case of VEVODAR ™,the oil itself is used as a raw material for feed formulations. In the case of AQUAGROW™ AA, the oil is mixed in with a feed matrix and provided as a novel feed formulation. No other sources of ARA have been anticipated as being acceptable for feeds or feed applications to date.
A few microalgae are known to produce ARA, although this is highly unusual in the marine environment. Such microalgae include, but are not limited to, Euglenophytes (e.g. Euglena), Rhodophytes (e.g., Porphyridium), and Chlorophytes (e.g., Parietochlods). Certain macroalgae (seaweeds) are also known to produce ARA. Such algae, or extracts thereof, would provide a beneficial diet for marine animals as whole algae, broken algae, or extracted material.
Certain crustaceans (e.g., brine shrimp, Artemia) or other zooplankton (e.g., rotifers) are used as feeds for various aquaculture crops (e.g., fish or shrimp) as they represent live feed for important first larval stages. In many cases, the Artemia are “loaded” with certain microalgae, which are carried into the larval animal through the consumption of the Artemia. In this way, certain beneficial nutrients, including ARA, can be provided from the algae to the larvae through the feed.